6. Yellowstone National Park, Wyoming/Idaho/Montana
In 1872, the Yellowstone National Park became the very first national park in the world. The more than 300 geysers that can be found in the park was the result of a super volcanic eruption that occurred more than 600,000 years ago. The most famous of all the geysers in the park is the geyser nicknamed “Old Faithful.” In just one and a half hour, the Old Faithful spews more than 8,000 gallons of boiling water. Yellowstone National Park is also a wildlife haven. Grizzly bears, moose, elks, and sometimes bison are often seen roaming inside the park freely.